Thin-film magnetic memory device executing data writing with data write magnetic fields in two directions

ABSTRACT

A tunneling magneto-resistance element forming an MTJ memory cell has an elongated form having an aspect ratio larger than one for stabilizing the magnetization characteristics. Bit lines and write word lines for carrying data write currents are arranged along short and long sides of the tunneling magneto-resistance element, respectively. The data write current flowing through the bit line, which can easily have an interconnection width, is designed to be larger than the data write current flowing through the write word line. For example, a distance between the write word line and the tunneling magneto-resistance element is smaller than a distance between the bit line and the tunneling magneto-resistance element.

This application is a continuation of application Ser. No. 10/134,523filed Apr. 30, 2002, now U.S. Pat. No. 6,903,963.

BACKGROUND OF THE INVENTION

The present invention relates to a thin-film magnetic memory device, andparticularly to a random access memory provided with memory cells havingMTJs (magnetic tunnel junctions)

DESCRIPTION OF THE BACKGROUND ART

Attention is being given to an MRAM (Magnetic Random Access Memory)device as a memory device, which can nonvolatilely store data with a lowpower consumption. The MRAM device is a memory device, in which aplurality of thin-film magnetic elements are formed in a semiconductorintegrated circuit for nonvolatilely storing data, and random access toeach thin-film magnetic elements is allowed.

Particularly, in recent years, it has been announced that a performanceof the MRAM device can be dramatically improved by using the thin-filmmagnetic members, which utilize the MTJs (magnetic tunnel junctions), asmemory cells. The MRAM device with memory cells having the magnetictunnel junctions has been disclosed in technical references such as “A10 ns Read and Write Non-Volatile Memory Array Using a Magnetic TunnelJunction and FET Switch in Each Cell”, ISSCC Digest of Technical Papers,TA7.2, February 2000, “Nonvolatile RAM based on Magnetic Tunnel JunctionElements”, ISSCC Digest of Technical Papers, TA7.3, February 2000, and“A 256 kb 3.0V 1T1MTJ Nonvolatile Magnetoresistive RAM”, ISSCC Digest ofTechnical Papers, TA7.6, February 2001.

FIG. 26 conceptually shows a structure of a memory cell, which has amagnetic tunnel junction, and may be merely referred to as an “MTJmemory cell” hereinafter.

Referring to FIG. 26, a MTJ memory cell includes a tunnelingmagneto-resistance element TMR having an electric resistance, which isvariable in accordance with a level of storage data, and an accesselement ATR for forming a path of a sense current Is passing throughtunneling magneto-resistance element TMR in a data read operation.Access element ATR is typically formed of a field-effect transistor, andtherefore may be referred to as an “access transistor ATR” hereinafter.Access transistor ATR is coupled between tunneling magneto-resistanceelement TMR and a fixed voltage (ground voltage Vss).

For the MTJ memory cell, the structure includes a write word line WWLfor instructing data writing, a read word line RWL for executing datareading and a bit line BL, which is a data line for transmitting anelectric signal in accordance with the data level of the storage data.

FIG. 27 conceptually shows an operation of reading data from the MTJmemory cell.

Referring to FIG. 27, tunneling magneto-resistance element TMR has aferromagnetic layer, which has a fixed and uniform magnetizationdirection, and may be merely referred to as a “fixed magnetic layer”hereinafter, and a ferromagnetic layer VL, which is magnetized in adirection depending on an externally applied magnetic field, and may bemerely referred to as a “free magnetic layer” hereinafter. A tunnelingbarrier (tunneling film) TB formed of an insulator film is disposedbetween fixed magnetic layer FL and free magnetic layer VL. Freemagnetic layer VL is magnetized in the same direction as fixed magneticlayer FL or in the opposite direction in accordance with the level ofthe storage data to be written. Fixed magnetic layer FL, tunnelingbarrier TB and free magnetic layer VL form a magnetic tunnel junction.

In the data read operation, access transistor ATR is turned on inresponse to activation of read word line RWL. Thereby, sense current Iscan flow through a current path formed of bit line BL, tunnelingmagneto-resistance element TMR, access transistor ATR and ground voltageVss.

Tunneling magneto-resistance element TMR has an electric resistance,which is variable depending on a correlation in magnetization directionbetween fixed magnetic layer FL and free magnetic layer VL. Morespecifically, when the fixed magnetic layer FL and free magnetic layerVL are magnetized in the same (parallel) direction, the electricresistance of tunneling magneto-resistance element TMR is smaller thanthat in the case where these layers FL and VL are magnetized in theopposite directions (non-parallel), respectively.

Accordingly, by magnetizing free magnetic layer VL in a directiondepending on the storage data, the voltage change caused in tunnelingmagneto-resistance element TMR by sense current Is changes depending onthe storage data level. For example, if sense current Is is passedthrough tunneling magneto-resistance element TMR after precharging bitline BL to a predetermined voltage, the storage data of the MTJ memorycell can be read out by detecting the voltage on bit line BL.

FIG. 28 conceptually shows an operation of writing data in the MTJmemory cell.

Referring to FIG. 28, read word line RWL is inactive, and accesstransistor ATR is off in the data write operation. In this state, thedata write currents for magnetizing free magnetic layer VL in thedirection depending on the level of the write data are supplied to writeword line WWL and bit line BL, respectively. The magnetization directionof free magnetic layer VL depends on the respective data write currentsflowing through write word line WWL and bit line BL.

FIG. 29 conceptually shows a relationship between the data write currentand the magnetization direction of the tunneling magneto-resistanceelement in the data write operation for the MTJ memory cell.

Referring to FIG. 29, an abscissa H(EA) gives a magnetic field, which isapplied in a easy axis (EA) to free magnetic layer VL of tunnelingmagneto-resistance element TMR. An ordinate H(HA) indicates a magneticfield acting in a hard axis (HA) on free magnetic layer VL. Magneticfields H(EA) and H(HA) correspond to two magnetic fields produced bycurrents flowing through bit line BL and write word line WWL,respectively.

In the MTJ memory cell, the fixed magnetization direction of fixedmagnetic layer FL is along the easy axis of free magnetic layer VL, andfree magnetic layer VL is magnetized along the easy axis direction, andparticularly in the same parallel direction, which is the same directionas fixed magnetic layer FL, or in the opposite parallel direction, whichis opposite to the above direction, depending on the level “1” or “0”)of the storage data. In the following description, the electricresistances of tunneling magneto-resistance element TMR, whichcorrespond to the two magnetization directions of free magnetic layerVL, are indicated by R1 and R0(R1>R0), respectively. The MTJ memory cellcan selectively store data (“1” and “0”) of one bit corresponding to thetwo magnetization directions of free magnetic layer VL.

The magnetization direction of free magnetic layer VL can be rewrittenonly when a sum of applied magnetic fields H(EA) and H(HA) falls withina region outside an asteroid characteristic line shown in FIG. 29.Therefore, the magnetization direction of free magnetic layer VL doesnot change when the data write magnetic fields applied thereto haveintensities corresponding to a region inside the asteroid characteristicline.

As can be seen from the asteroid characteristic line, the magnetizationthreshold required for changing the magnetization direction along themagnetization easy axis can be lowered by applying the magnetic field inthe direction of the hard axis to free magnetic layer VL.

When the operation point in the data write operation is designed, forexample, as shown in FIG. 29, the data write magnetic field in the MTJcell selected as a data write target is designed such that the datawrite magnetic field in the direction of the easy axis has an intensityof H_(WR). Thus, the data write current flowing through bit line BL orwrite word line WWL is designed to take a value, which can provide thedata write magnetic field of H_(WR). In general, data write magneticfield H_(WR) is represented by a sum of a switching magnetic fieldH_(SW) required for switching the magnetization direction and a marginΔH. Thus, it is represented by an expression of H_(WR)=H_(SW)+ΔH.

For rewriting the storage data of the MTJ memory cell, i.e., themagnetization direction of tunneling magneto-resistance element TMR, itis necessary to pass the data write currents at a predetermined level orhigher through write word line WWL and bit line BL. Thereby, freemagnetic layer VL in tunneling magneto-resistance element TMR ismagnetized in the same parallel direction as fixed magnetic layer FL oropposite parallel direction in accordance with the direction of the datawrite magnetic field along the easy axis (EA). The magnetizationdirection, which was once written into tunneling magneto-resistanceelement TMR, and thus the storage data of MTJ memory cell is heldnonvolatilely until next data writing is executed.

As described above, the electric resistance of tunnelingmagneto-resistance element TMR is variable in accordance with themagnetization direction, which is rewritable by the data write magneticfield applied thereto. Therefore, nonvolatile data storage can beexecuted by establishing a correlation between two magnetizationdirections of free magnetic layer VL in tunneling magneto-resistanceelement TMR and levels (“1” and “0”) of the storage data.

The references described before have disclosed technologies forintegrating such MTJ memory cells on a semiconductor substrate toprovide an MRAM device, which is a random access memory.

FIG. 30 conceptually shows a structure of a memory array formed of MTJmemory cells arranged in rows and columns.

Referring to FIG. 30, MTJ memory cells arranged in rows and columns canprovide a MRAM device of a high density. FIG. 30 shows the MTJ memorycells arranged in n rows and m columns (n, m: natural numbers). For the(n×m) MTJ memory cells arranged in rows and columns, the device isprovided with write word lines WWL1–WWLn of n in number and read wordlines RWL1–RWLn of n in number as well as bit lines BL1–BLm of m innumber. When the data write current flows in the data write operation,write word lines WWL1–WWLn are arranged in the row direction, and bitlines BL1–BLm are arranged in the column direction.

However, it is desired for stabilizing the magnetic characteristics thatthe tunneling magneto-resistance element used as the MTJ memory cell hasan elongated form having an aspect ratio (length-to-width ratio) largerthan one. Accordingly, the form of tunneling magneto-resistance elementTMR and the arrangement of the interconnection groups (write word linesand bit lines) for passing the data write currents must be designed tomatch with each other. Otherwise, a current density of theseinterconnection groups increases to cause a factor such aselectro-migration, which impedes operation reliability of the MRAMdevice.

In the operation of writing data into the MTJ memory cell, and thusrewriting the magnetization direction of the tunnelingmagneto-resistance element, the data write magnetic fields in the twodirections are applied as already described with reference to FIG. 29.If the data write magnetic field does not appropriately change withtime, therefore, the magnetizing operation may become unstable, and amalfunction may occur.

In a so-called “page mode operation” performed for increasing anoperation speed of a Dynamic Random Access Memory (DRAM), a plurality ofcolumn addresses are continuously and randomly accessed without changingthe row selection. For applying a similar page mode operation to theMRAM, therefore, it is necessary to design the device with considerationgiven to the data write characteristics of the MTJ memory cells alreadydescribed.

SUMMARY OF THE INVENTION

An object of the invention is to provide a thin-film magnetic memorydevice, which matches with a form of an MTJ memory cell having stablemagnetization characteristics, and operates stably.

Another object of the invention is to provide a structure of a thin-filmmagnetic memory device, which can stably and rapidly perform a page modeoperation.

A thin-film magnetic memory device according to the invention includes aplurality of memory cells each having a magnetic memory portion havingan electric resistance varying in accordance with a magnetizationdirection rewritable in response to application of a predetermined datawrite magnetic field caused by first and second data write currents; afirst data write interconnection arranged in a first direction forpassing the first data write current; and a second data writeinterconnection arranged in a second direction for passing the seconddata write current. The first data write current is larger than thesecond data write current, and the first data write interconnection hasa sectional area larger than a sectional area of the second data writeinterconnection.

Preferably, the first and second data write interconnections arearranged such that a distance between the first data writeinterconnection and the magnetic memory portion is longer than adistance between the second data write interconnection and the magneticmemory portion.

Preferably, the first data write interconnection has an interconnectionwidth larger than that of the second data write interconnection.

Preferably, the first data write interconnection has an interconnectionthickness larger than that of the second data write interconnection.

In the thin-film magnetic memory device described above, the data writeinterconnections for producing the data write magnetic fields can bearranged to prevent such a situation that a current density of one kindof the interconnections increases to impair operation reliability.

Preferably, each of the magnetic memory portions has a form having anaspect ratio larger than one between a long side and a short side. Thefirst data write interconnection has an interconnection width in thedirection of the long side, and the second data write interconnectionhas an interconnection width in the direction of the short side smallerthan that of the first data write interconnection.

Therefore, the device can employ the magnetic memory portion having aform designed to provide stable magnetization characteristics, andfurther the interconnection groups for passing the data write currentscan be arranged efficiently without lowering the operation reliabilityand increasing-a memory array area.

More preferably, the second data write interconnection-is arranged usinga metal interconnection layer at a higher level than the first datawrite interconnection.

Thereby, the structure can be easily applied to a memory device of alogic embedded type such as a system LSI (Large Scale Integratedcircuit).

According to another aspect of the invention, a thin-film magneticmemory device includes a plurality of memory cells each having amagnetic memory portion having an electric resistance varying inaccordance with a magnetization direction rewritable in response toapplication of a data write magnetic field; a first data writeinterconnection for passing a first data write current producing thedata write magnetic field along a easy axis; and a second data writeinterconnection for passing a second data write current producing thedata write magnetic field along a hard axis. The first data writecurrent has a rising time constant larger than a rising time constant ofthe second data write current at a start of a data write operationperformed by rewriting a magnetization direction of the magnetic memoryportion.

According to the thin-film magnetic memory device described above, amagnetic field applied in the direction of the hard axis to the memorycell can be produced more rapidly than a magnetic field in the directionof the easy axis at the start of data writing. Thereby, the magneticmemory portion of the memory cell selected as a data write target can bemagnetized stably.

Preferably, supply of the second data write current ends more early thanending of supply of the first data write current at the end of the datawrite operation.

At the end of the data write operation, therefore, it is possible toprovide a period, for which the data write magnetic field in thedirection of the hard axis decreases while the data write magnetic fieldat a predetermined level in the direction of the easy axis is beingapplied. Thereby, the magnetic memory portion of the memory cellselected as a data write target can be magnetized more stably.

More preferably, each of the magnetic memory portions has a form havingan aspect ratio larger than one between a long side and a short side.The first data write interconnection is arranged along the short side,and the second data write interconnection is arranged along the longside.

Thereby, it is possible to design the form of the magnetic memoryportion to provide stable magnetization characteristics, and theinterconnection groups for passing the data write current can bearranged efficiently.

Preferably, the plurality of memory cells are arranged in rows andcolumns, the first data write interconnections are arranged for thememory cell columns, respectively, and the second data writeinterconnections are arranged for the memory cell rows, respectively.The thin-film magnetic memory device further includes column selectlines arranged for the memory cell columns, respectively, and columnselect line drive portions arranged for the memory cell columns,respectively, each for driving a corresponding one of the column selectlines from a first voltage to a second voltage by a predeterminedoperation current in a selected column. The predetermined operationcurrent is set to provide the first data write current having the risingtime constant larger than the rising time constant of the second datawrite current.

More preferably, the column select line drive portion includes a drivegate portion for driving the corresponding column select line by one ofthe first and second voltages in accordance with results of columnselection, and a drive current switching portion for supplying a firstcurrent as the predetermined operation current to the drive gate portionin the data write operation, and supplying a second current larger thanthe first current as the predetermined operation current to the drivegate portion in the data read operation.

Thereby, the column select line of the selected column can be drivenrapidly in the data read operation so that the data reading can beperformed further rapidly.

According to still another aspect, the invention provides a thin-filmmagnetic memory device for executing a page mode operation with a unitoperation cycle including a row cycle for receiving input of a rowaddress and a plurality of subsequent column cycles for receiving inputof a column address in each of the column cycles, including a pluralityof memory cells arranged in rows and columns, and each having a magneticmemory portion having an electric resistance varying in accordance witha magnetization direction rewritable in response to application of apredetermined data write magnetic field produced by first and seconddata write currents; a plurality of first data write interconnectionsprovided for memory cell rows, respectively, for passing the first datawrite current in a selected row; a plurality of second data writeinterconnections provided for memory cell columns, respectively, forpassing the second data write current in a selected column; and a rowselect portion for controlling supply of the first data write current tothe plurality of data write interconnections. The row select portiontemporarily stops supply of the first data write current correspondingto the selected row in response to every ending of the column cycle.

Preferably, the row select portion includes a latch circuit for holdingrow selection results corresponding to the row address applied in therow cycle, and a drive unit for activating the first data writeinterconnection corresponding to the selected row to pass the first datawrite current in accordance with the row selection results held by thelatch circuit and a control signal for selectively instructing a datawrite operation and the data read operation.

Thereby, supply of the data write current corresponding to the selectedrow is temporarily stopped upon every ending of the column cycle in thepage mode operation. Therefore, the page mode operation can be executedstably and rapidly with low possibility of erroneous data writing.

Preferably, one of the first and second data write currents produces amagnetic field along a easy axis in the magnetic memory portion, and theother of the first and second data write currents produces a magneticfield along a hard axis in the magnetic memory portion. In each of thecolumn cycles including instruction of the data write operation, arising time constant of the one of the data write currents is largerthan that of the other data write current.

Preferably, each of the magnetic memory portions has a form having anaspect ratio larger than one between a long side and a short side, andone of the first and second data write interconnections carrying the oneof the data write current is arranged along the short side. Other of thefirst and second data write interconnections carrying the other datawrite current is arranged along the long side.

Accordingly, a magnetic field applied in the direction of the hard axisto the memory cell can be produced more rapidly than a magnetic field inthe direction of the easy axis at the start of data writing. Thereby,the magnetic memory portion of the memory cell selected as a data writetarget can be magnetized stably in each of the column cycles includinginstruction of the data writing.

Preferably, one of the first and second data write currents produces themagnetic field along a easy axis in the magnetic memory portion, and theother of the first and second data write currents produces a magneticfield along a hard axis in the magnetic memory portion. In each of thecolumn cycles including instruction of a data write operation, supply ofthe one of the data write currents starts later than the supply of theother data write current.

Thereby, it is possible to design the magnetic memory portion having aform providing stable magnetization characteristics, and theinterconnection groups for passing the data write currents can bearranged efficiently.

More preferably, each of the magnetic memory portions has a form havingan aspect ratio larger than one between a long side and a short side,and the one of the first and second data write interconnections carryingthe one of the data write currents is arranged along the short side. Theother of the first and second data write interconnections carrying theother data write current is arranged along the long side.

Thereby, the data read operation and the data write operation can becombined arbitrarily with each other for execution in each column cycleduring one page mode operation.

According to yet another aspect, the invention provides a thin-filmmagnetic memory device for executing a page mode operation with a unitoperation cycle including a row cycle for receiving input of a rowaddress and a plurality of subsequent column cycles for receiving inputof a column address in each of the column cycles, including a pluralityof memory cells arranged in rows and columns. Each of the memory cellshas a magnetic memory portion having an electric resistance varying inaccordance with a magnetization direction rewritable in response toapplication of a predetermined data write magnetic field produced byfirst and second data write currents, and an access element electricallycoupled in series to the magnetic memory portion, and being selectivelyturned on for passing a data read current. The thin-film magnetic memorydevice further includes a plurality of data write select lines providedcorresponding to the memory cell rows, respectively, and beingselectively activated to pass the first data write current; a pluralityof data read select lines provided corresponding to the memory cellrows, respectively, and being selectively activated to turn on theaccess element; a plurality of data lines provided corresponding to thememory cell columns, respectively; a read/write control circuit forsupplying the data read current to the data line corresponding to thereceived column address in each of the column cycles includinginstruction of a data read operations, and supplying the second datawrite current to the data line corresponding to the received columnaddress in each of the column cycles including instruction of a datawrite operation; and a row select portion for controlling activation ofthe plurality of first data write interconnections and the plurality ofdata read select interconnections in accordance with results of the rowselection based on the row address. The row select portion inactivatesthe data read select line corresponding to the selected row, andactivates the first data write interconnection corresponding to theselected row for a predetermined period in each of the column cyclesincluding instruction of the data write operation.

The thin-film magnetic memory device described above maintains theactive state of the data read select line in the selected row during aperiod except for the predetermined period of the column cycle, in whichthe data write operation is instructed. Therefore, an operation speedcan be increased in each column cycle including the instruction of theread operation.

Preferably, the row select portion activates the data read select linecorresponding to the selected row during a period other than thepredetermined period.

Preferably, each of the memory cells is arranged to have a nodeelectrically coupled to the corresponding first data writeinterconnection. The row select portion controls activation of theplurality of data read select lines such that the active period of thedata read select line may not overlap in time with the supply period ofthe first data write current.

Preferably, each of the memory cells is electrically isolated from thecorresponding first data write interconnection. The row select portioncontrols activation of the plurality of data read select lines such thatthe active period of each of the data read select lines has a portionoverlapping in time with the supply period of the second data writeselect current.

According to further another aspect, the invention provides a thin-filmmagnetic memory device for executing a page mode operation with a unitoperation cycle including a row cycle for receiving input of a rowaddress and a plurality of subsequent column cycles for receiving inputof a column address in each of the column cycles, including a pluralityof memory cells arranged in rows and columns. Each of the memory cellshas a magnetic memory portion having an electric resistance varying inaccordance with a magnetization direction rewritable in response toapplication of a predetermined data write magnetic field produced byfirst and second data write currents, and an access element electricallycoupled in series to the magnetic memory portion, and being selectivelyturned on for passing a data read current. The thin-film magnetic memorydevice further includes a plurality of data write select lines providedcorresponding to the memory cell rows, respectively, and beingselectively activated to pass the first data write current; a pluralityof data read select lines provided corresponding to the memory cellrows, respectively, and being selectively activated to turn on theaccess element; a plurality of data lines provided corresponding to thememory cell-columns, respectively; and a row select portion forcontrolling activation of the plurality of first data writeinterconnections and the plurality of data read select interconnectionsin accordance with results of the row selection based on the rowaddress. The row select portion activates the data read select linecorresponding to the selected row in the row cycle, and inactivates thedata read select line in the column cycle. The thin-film magnetic memorydevice further includes a read/write control circuit for supplying thedata read current to each of the data lines of at least M (M: integerlarger than one) in number among the plurality of data lines in the rowcycle, and supplying the second data write current to the data linecorresponding to the received column address in each of the columncycles including instruction of a data write operation; a read datalatch circuit for holding the storage data of M in number correspondingto the M data lines, respectively, and read from the memory cellsbelonging to the selected row in the row cycle; and a control circuitfor instructing output of one of the M storage data corresponding to thereceived column address to the read data latch circuit in each of thecolumn cycles including instruction of a data read operation.

In the thin-film magnetic memory device described above, the storagedata corresponding to the selected row is read in the row cycle, and isheld during the unit operation cycle. Therefore, the operation speed canbe increased in each of subsequent column cycles, in which the data readoperation is instructed.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a whole structure of an MRAMdevice according to a first embodiment of the invention;

FIG. 2 is a circuit diagram showing a structure of a memory array shownin FIG. 1;

FIG. 3 is an operation waveform diagram representing operations for datawriting and data reading in the memory array shown in FIG. 2;

FIG. 4 is a cross section showing a structure of a tunnelingmagneto-resistance element in an MTJ memory cell;

FIG. 5 conceptually shows an arrangement of bit lines BL and write wordlines WWL for the tunneling magneto-resistance element according to thefirst embodiment;

FIG. 6 shows a structure of the tunneling magneto-resistance elementaccording to the first embodiment;

FIG. 7 is a circuit diagram showing structures of a memory array and itsperipheral circuit according to a second embodiment;

FIG. 8 is a circuit diagram showing a structure of a data read circuitshown in FIG. 7;

FIG. 9 is a circuit diagram showing a structure of a data write circuitshown in FIG. 7;

FIG. 10 is a block diagram showing a structure of a column decoder shownin FIG. 7;

FIG. 11 is a circuit diagram showing a structure of a drive unit shownin FIG. 10;

FIG. 12 is a circuit diagram showing a structure of a write word linedriver;

FIG. 13A is an operation waveform diagram representing a data readoperation according to the second embodiment;

FIG. 13B is an operation waveform diagram representing a data writeoperation according to the second embodiment;

FIG. 14 conceptually shows magnetization behavior of the tunnelingmagneto-resistance element in the data write operation according to thesecond embodiment;

FIG. 15 shows occurrence of an undesired intermediate magnetizationstate occurring in a free magnetic layer during data writing;

FIG. 16 is a circuit diagram showing another example of the structure ofthe memory array;

FIG. 17 is an operation waveform diagram representing a page modeoperation for continuously executing data reading;

FIG. 18 is an operation waveform diagram showing a page mode operationfor continuously executing data writing;

FIG. 19 is a circuit diagram showing a structure of a word line driveraccording to a third embodiment;

FIG. 20 is an operation waveform diagram representing a data writeoperation in a page mode operation according to a first modification ofthe third embodiment;

FIG. 21 is a circuit diagram showing a structure of a drive unit of acolumn select line CSL according to the first modification of the thirdembodiment;

FIG. 22 is an operation waveform diagram showing a page mode operationaccording to a second modification of the third embodiment;

FIG. 23 is a circuit diagram showing a structure of a read word linedriver portion 30R according to the second modification of the thirdembodiment;

FIG. 24 is a whole block diagram showing a structure of an MRAM deviceaccording to a third modification of the third embodiment;

FIG. 25 is an operation waveform diagram representing a page modeoperation of MRAM device according to the third modification of thethird embodiment;

FIG. 26 conceptually shows a structure of an MTJ memory cell;

FIG. 27 conceptually shows an operation of reading data from the MTJmemory cell;

FIG. 28 conceptually shows an operation of writing data into the MTJmemory cell;

FIG. 29 conceptually shows a relationship between a data write currentand a magnetization direction of a tunneling magneto-resistance elementin the operation of writing data into the MTJ memory cell; and

FIG. 30 conceptually shows a structure of a memory array formed of MTJmemory cells arranged in rows and columns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will now be described with reference to thedrawings.

First Embodiment

Referring to FIG. 1, an MRAM device 1 according to a first embodiment ofthe invention executes random access in response to a control signal CMDand an address signal ADD, which are externally applied, and executesinput of write data DIN or output of read data DOUT. The data readoperation and data write operation in MRAM device 1 are executed inaccordance with timing, e.g., synchronized with an externally appliedclock signal CLK. Alternatively, MRAM device 1 may internally determinethe operation timing without receiving externally applied clock signalCLK.

MRAM device 1 includes a control circuit 5 for controlling a wholeoperation of MRAM device 1 in response to control signal CMD, and amemory array 10 having a plurality of MTJ memory cells arranged in rowsand columns. Memory array 10 includes a plurality of write word linesWWL and a plurality of read word lines RWL corresponding to rows of theMTJ memory cells, which may be merely referred to as “memory cell rows”hereinafter, although the structure of memory array 10 will be describedlater in greater detail. Also, bit lines BL and /BL are arrangedcorresponding to columns of the MTJ memory cells, which may be merelyreferred to as “memory cell columns” hereinafter.

MRAM device 1 further includes a row decoder 20, a column decoder 25, aword line driver 30 and read/write control circuits 50 and 60.

Row decoder 20 executes row selection in memory array 10 in accordancewith a row address RA represented by address signal ADD. Column decoder25 executes column selection in memory array 10 in accordance with acolumn address CA represented by address signal ADD. Word line driver 30selectively activates read word line RWL and write word line WWL basedon results of row selection of row decoder 20. Row address RA and columnaddress CA indicate the memory cell, which is designed or selected as atarget of data reading or writing, and may be referred to as a “selectedmemory cell” hereinafter.

Write word line WWL is coupled to a ground voltage Vss in a region 40spaced from word line driver 30 with memory array 10 therebetween.Read/write control circuits 50 and 60 collectively represent circuitgroups, which are arranged in regions neighboring to memory array 10 forsupplying data write currents and sense currents (data read currents) tobit lines BL and /BL in a selected memory cell column (which may bereferred to as a “selected column” hereinafter) corresponding to theselected memory cell.

Referring to FIG. 2, memory array 10 has MTJ memory cells MC arranged inn rows and m columns (n, m: natural numbers). In memory array 10, readword lines RWL1–RWLn as well as write word lines WWL1–WWLn are arrangedcorresponding to memory cell rows, respectively, and bit lines BL1–BLmare arranged corresponding to memory cell columns, respectively.

In the following description, reference character sets “WWL”, “RWL” and“BL” are used for collectively or generally indicating the write wordline(s), read word line(s) and bit line(s), respectively. Referencecharacter sets such as “WWL1”, “RWL1” and “BL1”, which include suffixesadded to the above sets, are used for specifically indicating the writeword line, read word line and bit line, respectively. A high voltagestate (power supply voltage Vcc) and a low voltage state (ground voltageVss) of each of signals and signal lines may be referred to as “H-level”and “L-level” hereinafter, respectively.

Each MTJ memory cell MC has a tunneling magneto-resistance element TMRoperating as a magnetic memory portion, of which electric resistance isvariable in accordance with a level of storage data, and an accesstransistor ATR operating as an access element and connected in series totunneling magneto-resistance element TMR. As already described, accesstransistor ATR is typically formed of an MOS transistor, which is afield-effect transistor formed on a semiconductor substrate.

Tunneling magneto-resistance element TMR is electrically coupled betweenaccess transistor ATR and corresponding write word line WWL. Accesstransistor ATR is electrically coupled between corresponding bit line BLand tunneling magneto-resistance element TMR.

A gate of access transistor ATR is coupled to corresponding read wordline RWL. Access transistor ATR is turned on to couple electricallytunneling magneto-resistance element TMR between corresponding bit lineBL and write word line WWL when read word line RWL is activated toattain H-level. When read word line RWL is inactive (L-level), accesstransistor ATR is turned off to isolate electrically bit line BL fromtunneling magneto-resistance element TMR.

Owing to the above structure, tunneling magneto-resistance element TMRand bit line BL are not coupled directly, but are coupled via accesstransistor ATR. Thereby, each bit line BL is not directly coupled to theplurality of tunneling magneto-resistance elements TMR belonging to thecorresponding memory cell column, but are electrically coupled only tothe tunneling magneto-resistance element of the selected memory cell,i.e., a data read target. Thereby, a capacitance of bit line BL can besmall, and an operation speed during data reading can be increased.

Further, tunneling magneto-resistance element TMR can be pulled down toground voltage Vss in the data read operation by using write word lineWWL. Therefore, it is not necessary to employ an interconnectiondedicated to supply of ground voltage Vss, and metal interconnectionsrequired for forming the MRAM device can be reduced in number.

Referring to FIG. 3, description will now be given on operations ofwriting and reading data in the memory array shown in FIG. 2.

First, operations for data writing are described. Word line driver 30activates and connects write word line WWL, which corresponds to theselected row, to power supply voltage Vcc in accordance with results ofrow selection of row decoder 20. An end of each write word line WWL iscoupled to ground voltage Vss in region 40. Therefore, write word lineWWL in the selected row carries a data write current Ip from word linedriver 30 toward region 40.

In the unselected row, write word line WWL can be maintained in aninactive state (L-level of ground voltage Vss) so that the data writecurrent does not flow. Each read word line RWL is maintained in aninactive state (L-level) in the data write operation.

Read/write control circuits 50 and 60 control the voltages on theopposite ends of bit line BL in the selected column, respectively, andthereby produce the data write current having a direction depending onthe data level of the write data. When storage data, e.g., of “1” is tobe written, the bit line voltage on the side of read/write controlcircuit 60 is set to a high voltage state (power supply voltage Vcc),and the bit line voltage on the opposite side, i.e., the side ofread/write control circuit 50 is set to a low voltage state (groundvoltage Vss). Thereby, data write current +Iw can be passed through thebit line in the selected column from read/write control circuit 60toward read/write control circuit 50.

When storage data of “0” is to be written, the voltage polarities of thebit line on the opposite sides, i.e., the sides of read/write controlcircuits 50 and 60 are inverted to flow a data write current ±Iw fromread/write control circuit 50 toward read/write control circuit 60.Thereby, data write current Ip and both data write currents ±Iw can besupplied so that the data write magnetic fields corresponding to thelevel of the write data can be applied to the selected memory cellselected as the data write target.

Description will now be given on the data read operation

In the data read operation, word line driver 30 activates read word lineRWL corresponding to the selected row to H-level in accordance withresults of the row selection of row decoder 20. In the unselected row,the voltage level of read word line RWL is kept inactive (at L-level),and each of write word lines WWL is kept at ground voltage Vss so thateach MTJ memory cell is pulled down to ground voltage Vss.

Bit line BL is precharged to ground voltage Vss before the data readoperation. In this state, the bit line in the selected column is pulledup by read/write control circuit 50, e.g., with power supply voltageVcc, and is supplied with a constant sense current Is.

When data reading starts, read word line RWL in the selected row isactivated to attain H-level, and corresponding access transistor ATR isturned on. Thereby, the MTJ memory cell corresponding to the selectedrow is electrically coupled between the bit line pulled up with powersupply voltage Vcc and write word line WWL at the level of groundvoltage Vss via access transistor ATR. Thereby, sense current Is passesthrough tunneling magneto-resistance element TMR of the selected memorycell. Therefore, voltage drop (ΔV0 or ΔV1 in FIG. 3) corresponding tothe level of the storage data of the selected memory cell occurs in theselected memory cell selected as the data read target.

Arrangement of the MTJ memory cell in the above MRAM device will now bedescribed.

Referring to FIG. 4, tunneling magneto-resistance element TMRcorresponding to the magnetic tunnel junction includes anantiferromagnetic material layer 101, a partial region of a fixedmagnetic layer 102 formed on antiferromagnetic material layer 101 andhaving a fixed magnetic field in a uniform direction, a free magneticlayer 103 magnetized by an applied magnetic field, a tunneling barrier104 made of an insulator film formed between fixed magnetic layer 102and free magnetic layer 103, and a contact electrode 105.

Antiferromagnetic material layer 101, fixed magnetic layer 102 and freemagnetic layer 103 are formed of appropriate magnetic materials such asFeMn or NiFe. Tunneling barrier 104 is formed of Al₂O₃ or the like.Tunneling magneto-resistance element TMR is electrically coupled to anupper interconnection via a barrier metal, which is arranged, ifnecessary, and is formed of a buffer member for electrical coupling tothe metal interconnection, although not shown.

Contact electrode 105 is electrically coupled to a lowerinterconnection. For example, the upper interconnection corresponds tobit line BL, and the lower interconnection corresponds to the metalinterconnection coupled to access transistor ATR.

Referring to FIG. 5, tunneling magneto-resistance element TMR has anelongated or rectangular form having an aspect ratio (i.e., a ratiobetween a long side length “a” and a short side length “b” in FIG. 5),which substantially falls within a range from 2:1 to 4:1. According tothis form, the easy axis (EA) and hard axis (HA) in the tunnelingmagneto-resistance element are parallel to the long side and the shortside, respectively.

Further, the rectangular form is chamfered to prevent occurrence ofunnecessary magnetization in the direction of hard axis (HA) in thevicinities of ends. As a result, it is possible to establish acorrelation between the two kinds of magnetization directions along theeasy axis in the free magnetic layer of the tunneling magneto-resistanceelement and the level of the write data, and thereby a data storingoperation can be performed with high reliability. In connection withthis, a threshold required for inverting magnetization in the directionof the easy axis can be lowered by applying a magnetic field in thedirection of the hard axis. In view of the above magnetizationcharacteristics, the operation point, i.e., the applied magnetic fieldin the data writing is set to be adapted to the case, where the datawrite currents in both the row and column directions are applied, asalready described with reference to FIG. 29.

As described above, the form of the tunneling magneto-resistanceelement, i.e., the form of the MTJ memory cell can be designed in viewof stability of the magnetization operation in the data write operation.Thereby, such a layout is naturally determined that bit line BL forgenerating the data write magnetic field in the direction of the easyaxis has an interconnection width larger than that of write word lineWWL for generating the magnetic field in the direction of the hard axis.Therefore, the area of the memory array can be reduced.

In other words, bit line BL has the interconnection width in thedirection of the long side, and write word line WWL has theinterconnection width in the direction of the short side. Therefore, itis easy to provide bit line BL having the interconnection width largerthan that of write word line WWL.

Referring to FIG. 6, access transistor ATR is formed at a p-type regionPAR on a semiconductor main substrate SUB. Access transistor ATR hassource/drain regions 110 and 120 formed of n-type regions as well as agate 130. Source/drain region 110 is coupled to bit line BL formed at afirst metal interconnection layer M1.

Read word line RWL is provided for controlling the gate voltage ofaccess transistor ATR, and it is not necessary to pass positively oractively a current therethrough. For increasing the density or degree ofintegration, read word line RWL is not formed at an independent metalinterconnection layer dedicated thereto, but is formed at the sameinterconnection layer as gate 130 by using a polycrystalline siliconlayer or a polycide structure.

Source/drain region 120 of access transistor ATR is electrically coupledto tunneling magneto-resistance element TMR via a metal film 150 formedin a contact hole, first metal interconnection layer M1 and a barriermetal 140. Barrier metal 140 is a buffer member provided forelectrically coupling tunneling magneto-resistance element TMR to themetal interconnection.

Write word line WWL is formed at a second metal interconnection layerM2, and is electrically coupled-to tunneling magneto-resistance elementTMR.

As described above, bit line BL and write word line WWL for carrying thedata write currents are arranged on the semiconductor substrate bearingthe MRAM device such that a distance between bit line BL, which has theinterconnection width in the direction of the long side of tunnelingmagneto-resistance element TMR, and tunneling magneto-resistance elementTMR is larger than a distance between write word line WWL, which has theinterconnection width in the direction of the short side of tunnelingmagneto-resistance element TMR, and tunneling magneto-resistance elementTMR.

Thus, the interconnection, which must carry a larger current in the datawrite operation, and is located relatively remote from tunnelingmagneto-resistance element TMR, is used as bit line BL, of whichinterconnection width can be increased easily. Thereby, it is possibleto lower a current density of write word line WWL, of whichinterconnection width cannot not be easily increased. In the MRAM deviceprovided with the MTJ memory cells having stable data writecharacteristics, therefore, the interconnection groups for passing thedata write currents can be efficiently arranged so as to preventlowering of the operation reliability.

A system LSI or the like, which has a memory and a logic embedded on acommon chip, is generally designed such that a metal interconnectionlayer at a higher level has a larger film thickness. By arranging writeword line WWL at a higher level as shown in FIG. 6, therefore, it iseasy to ensure an appropriate sectional area of write word line WWL,which cannot generally have an sufficient interconnection width due to arelationship to the form of tunneling magneto-resistance element TMR.Therefore, the MRAM device according to the first embodiment can beeasily applied to the memory device of a logic-embedded type.

In the structure shown in FIG. 6, bit line BL and thus metalinterconnection layer M1 may be designed to have large interconnectionthickness and film thickness, respectively, whereby it is possible toprevent increase in current density of bit line BL carrying a largerdata write current while reducing an interconnection width thereof. As aresult, the memory cell size can be reduced while giving considerationto the form of tunneling magneto-resistance element TMR.

Second Embodiment

In the data write operation, as already described in connection with thefirst embodiment, two kinds of data write magnetic fields are applied inthe directions of the hard axis and easy axis to the MTJ memory cell,respectively. A second embodiment will now be described in connectionwith a method of supplying the data write current for stably magnetizingthe tunneling magneto-resistance element forming each MTJ memory cell inthe data write operation.

Referring to FIG. 7, read word lines RWL1–RWLn as well as write wordlines WWL1–WWLn in a memory array according to the second embodiment arearranged corresponding to the memory cell columns similarly to thememory array shown in FIG. 2, respectively. Bit lines BL1 and /BL1–BLmand /BLm are arranged to form bit line pairs BLPI–BLPm corresponding tomemory cell columns, respectively. In the following description, bitlines /BL1–/BLm may be collectively represented as “bit lines IBL”.

MTJ memory cells MC in alternate rows are connected to the same kind ofbit lines BL or /BL. For example, among the MTJ memory cells belongingto the first memory cell column, the MTJ memory cell in the first row iscoupled to bit line /BL1, and the MTJ memory cell in the second row iscoupled to bit line BL1. The other MTJ memory cells are connected in asimilar manner so that the memory cells in each of the odd-numbered rowsare connected to one kind of bit lines /BL1–/BLm in the bit line pairs,respectively, and the MTJ memory cells in each of the even-numbered rowsare connected to the other kind of the bit lines BL1–BLm, respectively.

In the structure according to the second embodiment, memory array 10further has a plurality of dummy memory cells DMC coupled to bit linesBL1 and /BL1–BLm and /BLm. Dummy memory cells DMC are arranged in tworows and m columns so that each dummy memory cell DMC may correspond toeither dummy read word line DRWL1 or DRWL2. The dummy memory cellscorresponding to the dummy read word line DRWL1 are coupled to bit linesBL1, BL2, . . . and BLm, respectively. The other dummy memory cellscorresponding to dummy read word line DRWL2 are coupled to bit lines/BL1, /BL2, . . . and /BLm, respectively.

Dummy memory cell DMC has a dummy resistance element TMRd and a dummyaccess element ATRd. Dummy resistance element TMRd has an electricresistance Rd of a value intermediate between electric resistances Rmaxand Rmin, which correspond to storage data levels “1” and “0” of MTJmemory cell MC, respectively, and satisfy a relationship ofRmax>Rd>Rmin. Dummy access element ATRd is typically formed of afield-effect transistor, similarly to the access element of the MTJmemory cell. Therefore, the dummy access element may be referred to as“dummy access transistor ATRd” hereinafter.

Further, dummy write word lines DWWL1 and DWWL2 are arrangedcorresponding to each-row of the dummy memory cells. Depending on thestructure of dummy resistance element TMRd, the dummy write word linemay be unnecessary, but dummy write word lines DWWL1 and DWWL2 havingthe same design as write word lines WWL are provided for ensuringcontinuity of the forms or configurations on the memory array, andthereby avoiding complication of manufacturing processes.

In the data read operation, when an odd-numbered row is selected inaccordance with results of the row selection, each of bit lines/BL1–/BLm is coupled to MTJ memory cell MC. In this case, dummy readword line DRWL1 is activated, and each of bit lines BL1–BLm is coupledto dummy memory cell DMC. When an even-numbered row is selected and eachof bit lines BL1–BLm is coupled to MTJ memory cell MC, dummy read wordline DRWL2 is activated, and each of bit lines /BL1–/BLm is coupled todummy memory cell DMC.

Dummy read word lines DRWL1 and DRWL2 may be collectively referred to as“dummy read word line(s) DRWL”.

Word line driver 30 couples an end of write word line WWL in theselected row to a power supply voltage Vcc2 in the data write operation.Thereby, data write current Ip in the row direction can flow throughwrite word line WWL in the selected row in the direction from word linedriver 30 to region 40. The write word lines in the unselected rows arecoupled to ground voltage Vss by word line driver 30.

In the data read operation, word line driver 30 selectively activatesread word line RWL and dummy read word lines DRWL1 and DRWL2 to H-level(power supply voltage Vcc1) in accordance with results of the rowselection. More specifically, when an odd-numbered row is selected toconnect the MTJ memory cell group in the selected row to bit lines/BL1–/BLm, dummy read word line DRWL1 is activated to connect the dummymemory cell group to bit lines BL1–BLm. When an even-numbered row isselected, dummy read word line DRWL2 is activated.

Column select lines CSL1–CSLm for executing the column selection arearranged corresponding to the memory cell columns, respectively. Columndecoder 25 activates one of column select lines CSL1–CSLm to theselected state (H-level) in accordance with results of decoding ofcolumn address CA, i.e., results of the column selection in each of thedata write operation and data read operation.

Further, a data bus pair DBP is arranged for transmitting the read andwrite data. Data bus pair DBP includes data buses DB and /DBcomplementary to each other.

Read/write control circuit 50 includes a data write circuit 51W, a dataread circuit 51R and column select gates CSG1–CSGm, which are providedcorresponding to the memory cell columns, respectively.

Since each of column select gates CSG1–CSGm has a similar structure,description will now be representatively given on the structure ofcolumn select gate CSG1 provided for bit lines BL1 and /BL1.

Column select gate CSG1 has a transistor switch electrically coupledbetween data bus DB and bit line BL1, and a transistor switchelectrically coupled between data bus /DB and bit line /BL1. Thesetransistor switches are turned on and off in accordance with the voltageon column select line CSL1. When column select line CSL1 is activated toattain the selected state (H-level), column select gate CSG1electrically couples data buses DB and /DB to bit lines BL1 and /BL1,respectively.

In the following description, column select lines CSL1–CSLm and columnselect gates CSG1–CSGm will be collectively and merely referred to as“column select line(s) CSL” and “column select gate(s) CSG”,respectively.

Read/write control circuit 60 has short-circuit switch transistors62-1–62-m as well as control gates 66-1–66-m, which are providedcorresponding to the memory cell columns, respectively. Read/writecontrol circuit 60 further has precharge transistors 64-1 a and 64-1b–64-ma and 64-mb, which are arranged between ground voltage Vss and bitlines BL1 and /BL1–BLm and /BLm, respectively.

In the following description, short-circuit transistors 62-1–62-m,precharge transistors 64-1 a and 64-1 b–64-ma and 64-mb, and controlgates 66-1–66-m may be collectively referred to as “short-circuittransistor(s) 62”, “precharge transistor(s) 64” and “control gate(s)66”.

Each control gate 66 outputs results of logical AND betweencorresponding column select line CSL and control signal WE. Therefore,the output of control gate 66 corresponding to the selected column isselectively activated to attain H-level in the data write operation.

Short-circuit switch transistor 62 is turned on/off in response to theoutput of corresponding control gate 66. In the data write operation,therefore, short-circuit switch transistor 62 electrically couples endson one side of bit lines BL and /BL corresponding to the selected columnto each other.

Each precharge transistor 64 is turned on to precharge bit lines BL1 and/BL1–BLm and /BLm to ground voltage Vss in response to activation of abit line precharge signal BLPR. Bit line precharge signal BLPR producedby control circuit 5 is activated to attain H-level for at least apredetermined period before execution of the data reading while MRAMdevice 1 is active. While MRAM device 1 is active, and particularly inthe data read operation and data write operation, bit line prechargesignal BLPR is inactivated to attain L-level, and precharge transistor64 is turned off.

Description will now be given on the structures of the data read circuitand the data write circuit.

Referring to FIG. 8, data read circuit 51R includes constant-currentsupply circuits 70 and 71, which receive power supply voltage Vcc1 andsupply a constant current I(Read) to internal nodes Ns1 and Ns2,respectively, an N-channel MOS transistor 73 electrically coupledbetween internal node Ns1 and data bus DB, an N-channel MOS transistor74 electrically coupled between internal node Ns2 and data bus /DB, anamplifier 75 for amplifying a voltage level difference between internalnodes Ns1 and Ns2 to output read data DOUT, and resistances 76 and 77.

Each of N-channel MOS transistors 73 and 74 receives reference voltageVrr on its gate. Resistances 76 and 77 are provided for pulling downinternal nodes Ns1 and Ns2 to ground voltage Vss, respectively. Owing tothis structure, data read circuit 51R can supply sense current Iscorresponding to constant current I(Reed) to each of data buses DB and/DB in the data read operation.

In the data read operation, each of data buses DB and /DB is pulled downto ground voltage Vss via one of bit lines BL and /BL and one of theselected memory cell and the dummy memory cell. Thereby, data readcircuit 51R can amplify the voltage difference between internal nodesNs1 and Ns2, and thereby can read out the storage data in the selectedmemory cell.

Referring to FIG. 9, data write circuit 51W has a constant-currentsupply circuit 80 for supplying a constant current I(write), andP-channel MOS transistors 81 and 82 forming a current mirror circuit.Thereby, the current supplied to an internal node Nw0 is set inaccordance with constant current I(write).

Data write circuit 51W further has inverters 84, 85 and 86, whichreceive an operation current via internal node Nw0. Each of inverters84, 85 and 86 receives power supply voltage Vcc2 and ground voltage Vss.

Inverter 84 inverts the voltage level of write data DIN, and transmitsthe same to data bus DB. Inverter 85 inverts the voltage level of writedata DIN, and transmits the same to an input node of inverter 86.Inverter 86 inverts the output of inverter 84, and transmits the same todata bus /DB. Therefore, data write circuit 51W sets the voltages ondata buses DB and /DB to power supply voltage Vcc2 and ground voltageVss in accordance with the level of write data DIN, respectively.

Thereby, data write current ±Iw in the direction depending on the levelof write data DIN can flow through a path formed of data bus DB (/DB),column select gate CSG, bit line BL (/BL), short-circuit switchtransistor 62, bit line /BL (BL), column select gate CSG and data bus/DB (DB) in the selected column.

Power supply voltage Vcc2, which is the operation voltage of data writecircuit 51W, is set higher than voltage Vcc1, which is the operationvoltage of data read circuit 51R. This is because data write currents Ipand ±Iw, which are required for magnetizing tunneling magneto-resistanceelement TMR of the selected memory cell in the data write operation, arelarger than sense current Is required for data reading. For example,power supply voltage Vcc2 may be formed of an external power supplyvoltage itself, which is externally supplied to MRAM device 1, and thisexternal power supply voltage may be lowered by a voltage drop converter(not shown) to generate power supply voltage Vcc1. By this structure,these power supply voltages Vcc1 and Vcc2 can be efficiently supplied.

Description will now be given on structures of the column decoder andthe word line driver.

Referring to FIG. 10, column decoder 25 has decode units CDU1–CDUm aswell as drive units DVU1–DVUm, which are provided corresponding to thememory cell columns, respectively. Each of decode units CDU1–CDUmreceives column address CA, and activates its output to attain L-levelwhen the corresponding memory cell column is selected. Drive unitsDVU1–DVUm drive column select lines CSL1–CSLm in response to the outputsof decode units CDU1–CDUm, respectively.

Drive units DVU1–DVUm have the same structure. Therefore, FIG. 11representatively shows only drive unit DVU1 corresponding to columnselect line CSL1.

Referring to FIG. 11, drive unit DVU1 has P-channel MOS transistors 200and 201 connected in series between power supply voltage Vcc1 and columnselect line CSL1, P-channel MOS transistors 202 and 203 connected inseries between power supply voltage Vcc2 and column select line CSL1,and an N-channel MOS transistor 204 connected between column select lineCSL1 and ground voltage Vss.

Drive unit DVU1 further has logic gates 206 and 208. Logic gate 206outputs results of logical AND between control signals /RE and /WR1.Control signal /WR1 is activated to attain L-level for a predeterminedperiod, during which column select line CSL in the selected column is tobe active, in the data write operation. For a period other than theabove, control signal /WR1 is inactive and at H-level. Control signal/RE is activated to attain L-level for a predetermined period in thedata read operation, and is kept inactive (H-level) for the period otherthan the above.

Logic gate 208 applies results of logical OR between the output of logicgate 206 and the output of decode unit CDU1 to each of the gates ofP-channel MOS transistors 201 and 203 and N-channel MOS transistor 204.P-channel MOS transistor 200 receives an inverted signal of controlsignal /WE on its gate, and P-channel MOS transistor 202 receivescontrol signal /WE on its gate.

P-channel MOS transistor 202 is designed to have a current drive powersmaller than that of P-channel MOS transistor 200. For example,P-channel MOS transistor 202 is designed to have a smaller gate widththan transistor 200 so that the above characteristics are achieved.

According to the above structure, an inverter formed of P- and N-channelMOS transistors 203 and 204, which are supplied with an operationcurrent I1 from turned-on P-channel MOS transistor 202, drives columnselect line CSL1 in accordance with the output of logic gate 208 in thedata write operation.

More specifically, when the output of decode unit CDU1 is active and atL-level, i.e., when the memory cell column in the first position isselected, column select line CSL1 is driven to H-level (power supplyvoltage Vcc2) in response to the active period (L-level) of controlsignal /WR1. Column select line CSL in the unselected column is drivento ground voltage Vss.

In the data read operation, an inverter formed of P- and N-channel MOStransistors 201 and 204, which are supplied with an operation current I2(I2>I1) from turned-on P-channel MOS transistor 200, drives columnselect line CSL1 in accordance with the output of logic gate 208.Therefore, selected column select line CSL1 is driven to H-level (powersupply voltage Vcc2) in response to the active period (L-level) ofcontrol signal /RE.

As described above, decode unit CDU1 outputs the results of decoding inaccordance with the same timing in both the data read operation and thedata write operation, but active column select line CSL is driven bydifferent drive powers (i.e., different amounts of supplied currents) inthe data write operation and the data read operation, respectively.Therefore, the voltage on column select line CSL, which is activated inthe data write operation, rises slowly, and has a large rising timeconstant. In the data read operation, the voltage on active columnselect line CSL rises fast, and thus has a small rising time constant.

Referring to FIG. 12, row decoder 20 has decode units RDU1–RDUn providedcorresponding to the memory cell rows, respectively. Each of decodeunits RDU1–RDUn receives row address RA, and activates its output toattain L-level when the corresponding memory cell row is selected.

Word line driver 30 includes a write word line drive portion 30W forcontrolling activation of write word lines WWL1–WWLn, and a read wordline drive portion 30R for controlling activation of read word linesRWL1–RWLn.

Write word line drive portion 30W includes drive gates 210-1–210-nprovided corresponding to write word lines WWL1–WWLn, respectively. Eachof drive gates 210-1–210-n is formed of an NOR gate receiving powersupply voltage Vcc2 and ground voltage Vss for operation. Drive gate210-1–210-n drive write word lines WWL1–WWLn in accordance with theoutputs (results of decoding) of respective decode units RDU1–RDUn andcontrol signal /WR2.

Control signal /WR2 is activated to attain L-level for a periodcorresponding to the period of the active state of write word line WWLin the selected row during the data write operation. For the periodother than the above, control signal /WR2 is inactive and at H-level.Control signals /WR1, /WR2 and /RE are produced, e.g., by controlcircuit 5. When starting the data write operation, control signals /WR1and /WR2 are activated (change from H-level to L-level) in accordancewith the same timing. However, when ending the data write operation,control signal /WR2 is inactivated (changes from L-level to H-level),and thereafter control signal /WR1 is inactivated.

Thereby, write word line WWL corresponding to the selected row is drivento power supply voltage Vcc2 (H-level) for passing data write current Ipfor a period of the L-level of control signal /WR2. However, write wordlines WWL in the unselected rows are kept at ground voltage Vss(L-level). For periods including the period of the data read operationbut not including the data write operation, control signal /WE is set toH-level, and each write word line WWL is inactive, and is set to groundvoltage Vss.

Read word line drive portion 30R includes drive gates 220-1–220-nprovided corresponding to read word lines RWL1–RWLn, respectively. Eachof drive gates 220-1–220-n is formed of an NOR gate receiving powersupply voltage Vcc1 and ground voltage Vss for operation. Drive gates220-1–220-n drive read word lines RWL1–RWLn in accordance with theoutputs (results of decoding) of respective decode units RDU1–RDUn andcontrol signal /RE.

In the data read operation performed with control signal /RE at L-level,read word line RWL corresponding to the selected row is driven toH-level (power supply voltage Vcc1) for turning on access transistorATR. Read word lines RWL in the unselected rows are kept at groundvoltage Vss (L-level). For periods including the period of the datawrite operation but not including the data read operation, controlsignal /RE is set to H-level, and each read word line RWL is inactive,and is set to ground voltage Vss.

Although not shown in FIG. 12, decode units and drive gates similar tothose for read word lines RWL are arranged for dummy read word linesDRWL1 and DRWL2.

FIGS. 13A and 13B are operation waveform diagrams representing the dataread operation and the data write operation according to the secondembodiment, respectively.

Referring to FIG. 13A, the data read operation starts in response to aread command applied in accordance with the activation timing of clocksignal CLK.

When the data read operation starts, read word line RWL in the selectedrow and column select line CSL in the selected column are activated inresponse to supplied row address RA and column address CA. The order ofactivation of read word line RWL and column select line CSL is notparticularly restricted, and these lines are activated in accordancewith the fastest timing for achieving fast access.

In particular, each of drive units DVU1–DVUm in column decoder 25 drivescolumn select line CSL by P-channel MOS transistor 200 (FIG. 11) havinga large drive current. Therefore, when the decode unit sends the resultsof decoding at a time t0, column select line CSL in the selected columnrises from L-level to H-level at a time t1.

In the data read operation, each write word line WWL is kept at thelevel of ground voltage Vss so that the data write current does not flowtherethrough. For bit lines BL and /BL in the selected column, constantsense current Is is supplied for the active period of column select lineCSL. Sense current Is passes through the tunneling magneto-resistanceelement in the selected memory cell via the access transistor, which isturned on in response to the activation of read word line RWL. Thereby,the change in voltage already described with reference to FIG. 3 occursso that the storage data can be read from the selected memory cell.

When ending the data read operation, column select line CSL in theselected column is inactivated at a time t4. In response to this, supplyof sense current Is to bit lines BL and /BL in the selected column ends.

Referring to FIG. 13B, the write command is applied in accordance withthe activation timing of clock signal CLK to start the data writeoperation, similarly to the data read operation.

When the data write operation starts, write word line WWL in theselected row is activated to carry data write current Ip in accordancewith applied row address RA. Data write current Ip reaches apredetermined level at a time tw.

Column select line CSL in the selected column is slowly driven byP-channel MOS transistor 202 (FIG. 11) having a small current drivepower. Therefore, the rising time constant of column select line CSL inthe data write operation is set to be larger than that in the data readoperation. More specifically, when the decode unit sends results of thedecoding at time t0, column select line CSL rises from L-level toH-level at a time t2 later than time t1. In FIG. 13A, an operationwaveform of the column select line in the selected column during thedata reading is depicted by dotted line for comparison.

Thereby, data write currents ±Iw flowing through bit lines BL and /BL inthe selected column start to flow slowly in accordance with the drivespeed of column select line CSL when starting the data write operation.More specifically, data write currents ±Iw flowing through bit lines BLand /BL in the selected column reach the predetermined levels at time t2later than time tw, at which data write current Ip reaches thepredetermined level. In other words, the drive power of column selectline CSL in the data write operation, i.e., operation current I1 shownin FIG. 11 is designed such that column select line CSL can be activatedin accordance with the above timing.

Owing to the above structure, the data write magnetic field in thedirection of the easy axis can be applied to the tunnelingmagneto-resistance element in the selected memory cell after applyingthe data write magnetic field in the direction of the hard axis whenstarting the data write operation.

When the data write operation is to be ended, write word line WWL in theselected row is inactivated at time t3 before time t4, at which columnselect line CSL in the selected column is inactivated, and thus supplyof data write currents ±Iw to bit lines BL and /BL in the selectedcolumn ends. Thereby, supply of data write current Ip ends. Morespecifically, the timing of inactivatation of control signal /WR1 shownin FIG. 11 is set in accordance with time t4, and the timing ofinactivatation of control signal /WR2 shown in FIG. 12 is set inaccordance with time t3. The timing of activation of each of controlsignals /WR1 and /WR2 is set in accordance with time t0.

Thereby, at the end of the data write operation, such a period can beprovided that the data write magnetic field is kept at a predeterminedlevel in the direction of the easy axis, and the data write magneticfield in the direction of the hard axis decreases.

FIG. 14 conceptually shows a behavior of the tunnelingmagneto-resistance element in the data write operation according to thesecond embodiment.

Referring to (a) in FIG. 14, the free magnetic layer in the tunnelingmagneto-resistance element is magnetized in a certain direction(rightward at (a) in FIG. 14) along the easy axis before time to ofstart of the data write operation (t<t0). Description will now be givenon the data write operation, in which the magnetization direction at (a)in FIG. 14 is rewritten to the opposite direction.

Referring to (b) in FIG. 14, data write current Ip flowing through writeword line WWL applies a data write magnetic field Hh along hard axis(HA) for a period (t=t0–t1) from time t0 to time t1. Thereby, themagnetization direction of the free magnetic layer starts to rotateslowly.

For a period (t=t1–t2) from time t1 to time t2, as shown at (c) in FIG.14, data write magnetic field Hh at a predetermined level is kept in thedirection of the hard axis, and further data write magnetic field He inthe direction of the easy axis is applied for inverting themagnetization direction of the free magnetic layer. When the sum of datawrite magnetic fields Hh and He reaches a region outside the asteroidcharacteristic line shown in FIG. 29, the direction of magnetization ofthe free magnetic layer is rewritten from the direction indicated by anarrow with dotted line to the direction indicated by an arrow with solidline.

For a period (t=t3–t4) from time t3 to time t4, as shown at (d) in FIG.14, data write magnetic field He at a predetermined level is kept in thedirection of the easy axis, and data write magnetic field Hh in thedirection of the hard axis decreases. Thereby, a vectorial sum of datawrite magnetic fields Hh and He changes and turns its direction as shownat (c) in FIG. 14 when the data write operation ends.

As indicated at (e) in FIG. 14, by changing data write magnetic fieldsHh and He in the above order, the magnetization direction of the freemagnetic layer is stably rewritten to the opposite direction in the datawrite operation without entering an undesirable intermediatemagnetization state.

Referring to FIG. 15, description will now be given on the undesirableintermediate magnetization state of the free magnetic layer in the datawrite operation.

Referring to FIG. 15, end regions 108 and 109 of tunnelingmagneto-resistance element TMR have such characteristics that theseregions are not easily magnetized in response to the magnetic fieldalong the easy axis, and the direction and amount (degree) of themagnetization gradually change. Therefore, the end regions havecharacteristics, which are undesirable for the memory cell, in contrastto a central region 107, in which the direction and amount ofmagnetization are determined in a binary manner in response to themagnetic field along the easy axis.

In the free magnetic layer of tunneling magneto-resistance element TMR,as shown at (a) and (b) in FIG. 15, the central region is magnetizedalong the easy axis and particularly in the direction depending on thelevel of write data after magnetizing end regions 108 and 109 in onedirection along the hard axis, whereby the free magnetic layer can havestable magnetization characteristics.

As described above, the activation of column select line CSL can bedelayed from the activation of write word line WWL, whereby the datawrite magnetic field in the direction of the hard axis is applied priorto the data write magnetic field in the direction of the easy axis.Thereby, the magnetization directions in end regions 108 and 109 oftunneling magneto-resistance element TMR can be set to a uniformdirection (upward at (a) and (b) in FIG. 15), and thereaftermagnetization in the direction of the easy axis can be inverted stablyin central region 107.

In contrast to the above, if column select line CSL is activatedsubstantially simultaneously with or prior to write word line WWL, thefree magnetic layer enters a multi-stable state, and is magnetized inirregular directions causing the intermediate state other than thedesired stable state, as shown at (c), (d) and (e) in FIG. 15.

As a result, the magnetization direction of the free magnetic layer andcannot be uniform after the data writing, and do not attain the desiredstate shown at (a) or (b) in FIG. 15. Therefore, a desired electricresistance difference corresponding to the difference in level of thestorage data cannot be ensured in the memory cell holding the writtendata. This causes a malfunction, and impairs the operation stability ofthe MRAM device.

As already described, by supplying the data write current in accordancewith the second embodiment, the data write magnetic field in thedirection of the hard axis can be produced or removed more rapidly thanthe data write magnetic field in the easy axis when starting and endingthe data write operation. Thereby, the data writing can be stablyexecuted in view of the magnetization characteristics of the MTJ memorycell.

The drive power of column select line CSL corresponding to the selectedcolumn can be switched between those for the data read operation and thedata write operation. Thereby, column select line CSL corresponding tothe selected column can be activated fast in accordance with earliesttiming in the data read operation so that the operation speed can beincreased. Also, in the data write operation, the data writing can bestably executed while avoiding the magnetically unstable intermediatestate. Thus, both the stable data writing and the fast data reading canbe achieved.

Although the tunneling magneto-resistance element shown in FIGS. 14 and15 has a rectangular form, the tunneling magneto-resistance element mayhave a chamfered form as already described in connection with the firstembodiment. Even in this case, the magnetization behavior in the datawrite operation is the same as that already described.

Memory array 10 may employ a structure other than that shown in FIG. 7for supplying the data write current according to the second embodiment.For example, the second embodiment may be employed in a memory array ofa structure shown in FIG. 16, in which each write word line WWL is notelectrically coupled to the MTJ memory cell, but access transistor ATRand tunneling magneto-resistance element TMR are connected in seriesbetween bit line BL and ground voltage Vss supply node.

The data reading and data writing can be performed similarly in such astructure that column select lines CSL dedicated to writing are employedindependently of column select lines CSL dedicated to reading.

Third Embodiment

A third embodiment will now be described in connection with a structurefor applying a page mode operation, which is used in a conventionaldynamic random access memory, to an MRAM device.

FIG. 17 is an operation waveform diagram representing a page modeoperation for continuously executing the data reading.

Referring to FIG. 17, one unit operation cycle of the page modeoperation includes a row cycle for receiving a row address used for therow selection, and a plurality of column cycles for continuouslyaccessing a plurality of columns while maintaining the row selectionperformed in the row cycle. In-each column cycle, the data readoperation or data write operation is instructed, and a column addressindicating the target of data reading or data writing is input.

Each of the row and column cycles starts in response to clock signalCLK. In the row cycle, row address RA for executing the row selection isinput. For example, memory array 10 is divided into a plurality ofbanks, and a bank address BA is further input together with row addressRA when the bank selection is further required for specifying theselected row.

In response to the level of control signal /WE, which is input in therow cycle, it is determined which operation between data reading anddata writing is to be executed in the subsequent column cycles. In FIG.17, since control signal /WE is at H-level when clock signal CLK becomesactive in the row cycle, the data read operation is executed in each ofthe subsequent column cycles. In each column cycle, a column cyclesignal /CC is activated to attain L-level for a predetermined periodbased on clock signal CLK.

In an example of operation shown in FIG. 17, the data reading iscontinuously performed in the column cycles. In the row cycle, read wordline RWL in the selected row is activated to change its level fromL-level to H-level in response to row address RA (and bank address BA).Activation of read word line RWL in the selected row is kept within thesame unit operation cycle.

In a column cycle #1, control signal /WE is set to H-level for apredetermined period. Further, a column address CA1 representing thedata read target is input. In response to column address CA1, columnselect line CSL in the selected column is activated in accordance withtiming similar to that shown in FIG. 13A. In response to this, bit lineBL in the selected column carries sense current Is to be passed throughthe tunneling magneto-resistance element in the selected memory cell.Thereby, storage data can be read from the selected memory cellcorresponding to row address RA (and bank address BA) and column addressCA1.

In a column cycle #2, data is likewise read from the selected memorycell corresponding to column address CA2 and row address RA (and bankaddress BA).

FIG. 18 is an operation waveform diagram representing the page modeoperation for continuously executing the data writing.

Referring to FIG. 18, when the data write operation is continuouslyexecuted in the column cycles, control signal /WE is set to L-level inthe row cycle. In response to this, each read word line RWL is kept inan inactive state (L-level of ground voltage Vss) in the row cycle andeach of the subsequent column cycles. The results of row selection,which is performed in response to row address RA (and bank address BA)applied in the row cycle, are held in the same unit operation cycle.

In each column cycle for executing the data writing, control signal /WEis set to L-level for a predetermined period. Activation of write wordline WWL in the selected row, which corresponds to row address RA (andbank address BA) applied in the row cycle, is controlled in each columncycle.

For example, column cycle signal /CC and a delayed signal of controlsignal /WE are used, and write word line WWL in the selected row isactivated to carry data write current Ip for a predetermined period(from time t0 to time t4 in FIG. 18) in column cycle #1 includingexecution of the data write operation. In periods other than the above,write word line WWL in the selected row is inactivated, and supply ofthe data write current ends. More specifically, when the row cycle andeach column cycle end, each write word line WWL is inactivated, andsupply of data write current Ip temporarily stops.

Thereby, it is possible to reduce the possibility of erroneous datawriting in the unit operation cycle of the page mode operation, ascompared with the structure maintaining the activation of write wordline WWL in the selected row. In other words, if the activation of thewrite word line in the selected row were maintained, the magnetic fieldat the predetermined level in the direction of the hard axis would becontinuously applied to each MTJ memory cell in the selected row. Thiswould result in a possibility that erroneous data writing is caused evenby magnetic noises of a smaller intensity.

In column cycle #1, column address CA1 is input as address signal ADD inaccordance with the timing of activation of dock signal CLK, and controlsignal /WE is set to L-level. Thereby, activation of column select lineCSL corresponding to column address /CA1 and supply of data writecurrent Ip for write word line WWL are executed in accordance with thetiming similar to that already described with reference to FIG. 17.Therefore, the data write operation in column cycle #1 is performedsimilarly to that in FIG. 13B, and the data write magnetic field in thedirection of the hard axis can be produced or removed more rapidly thanthe data write magnetic field in the direction of the easy axis when thedata write operation starts or ends. Thereby, the data writing can bestably executed with consideration given to the magnetizationcharacteristics of the MTJ memory cell.

Referring to FIG. 19, word line driver 30 according to the thirdembodiment includes latch circuits 260-1–260-n for latching results ofdecoding of decode units RDU1–RDUn, read word line drive portion 30R andwrite word line drive portion 30W.

Latch circuits 260-1–260-n latch outputs (results of decoding) of decodeunits RDU1–RDUn in response to control signal RC, which becomes activein accordance with predetermined timing in the row cycle. Thereby, latchcircuits 260-1–260-n hold the results of row selection corresponding torow address RA (and bank address BA), which is applied in the row cycle,within the same unit operation cycle.

Read word line drive portion 30R further has a latch circuit 250 inaddition to drive gates 220-1–220-n shown in FIG. 12. Latch circuit 250holds the signal level of control signal WE (i.e., inverted signal of/WE), which is applied in the row cycle, in response to control signalRC.

Contents held in latch circuit 250 and each of latch circuits260-1–260-n are renewed in, every row cycle within a new unit operationcycle.

Each of drive gates 220-1–220-n controls activation of correspondingread word line RWL in response to results of row selection held incorresponding one of latch circuits 260-1–260-n and control signal WEheld in latch circuit 250. As already described with reference to FIGS.17 and 18, therefore, the inactive state (L-level) of each read wordline RWL is maintained in the current row cycle and the subsequentcolumn cycle when control signal /WE is set to L-level (WE=“H”) in therow cycle.

When control signal /WE is set to H-level in the row cycle, the activestate (H-level) of read word line RWL in the selected row is maintainedin the current row cycle and the subsequent column cycle. Control of theactivation of read word line RWL is changed in response to controlsignal RC in every new row cycle. Although not shown in FIG. 19, similarstructures are employed for dummy read word lines DRWL1 and DRWL2.

Write word line drive portion 30W according to the third embodimentdiffers from the write word line drive portion shown in FIG. 12 in thatswitch transistors 212-1–212-n and a delay circuit 255 are furtheremployed.

Delay circuit 255 delays control signal /WE by a predetermined time tooutput a control signal /WEd. Further, switch transistors 212-1–212-nsupply an operation current to drive gates 210-1–210-n in response tocolumn cycle signal /CC shown in FIGS. 17 and 18, respectively.

Each of drive gates 210-1–210-n controls activation of correspondingwrite word line WWL in response to results of the row selection held incorresponding one of latch circuits 260-1–260-n, which are commonly usedby read word line drive portion 30R, and control signal /WEd sent fromdelay circuit 255. The delay time in delay circuit 255 is determined inview of the preferable supply timing of data write current Ip, i.e.,times t0 and t3 shown in FIG. 18.

Owing to the above structure, activation of write and read word linesWWL and RWL can be controlled in accordance with the appropriate timingfor executing the page mode operation shown in FIGS. 17 and 18. Forcolumn select line CSL, the activation control can be performed by thecolumn decoder, which has a structure similar to that of the secondembodiment.

According to the structure of the third embodiment, as described above,both the fast data reading and the stable data writing performed withconsideration given to the magnetization characteristics of the MTJmemory cell can be performed in the page mode operation for continuouslyexecuting either the data read operation or the data write operation.

First Modification of Third Embodiment

In a page mode operation according to a first modification of the thirdembodiment, as shown in FIG. 20, the word line driver shown in FIG. 19controls activation of write and read word lines WWL and RWL, wherebysupply timing of data write current Ip is set similarly to the timingshown in FIG. 18.

The page mode operation according to the first modification of the thirdembodiment shown in FIG. 20 differs from that shown in FIG. 18 in thatthe activation of column select line CSL in the selected column isdelayed in each column cycle including instruction of the data writing.More specifically, supply of data write currents ±Iw for producing thedata write magnetic field in the direction of the easy axis starts attime tw, and the level thereof increases to a predetermined level attime t2.

When the data write operation ends, the time of inactivatation of columnselect line CSL is set to time t4 later than time t3, which is the timeof inactivatation of write word line WWL.

The data write operation in a subsequent column cycle #2 is executed onthe selected memory cell, which corresponds to column address CA2applied in the same column cycle and row address RA (and bank addressBA) applied in the row cycle, similarly to column cycle #1.

According to the above data write operation, and particularly in thecolumn cycle for executing the data writing, supply of data writecurrents ±Iw for producing the data write magnetic field in thedirection of the easy axis starts and ends in accordance with the timingdelayed from the start and end of supply of data write current Ip forproducing the data write magnetic field in the direction of the hardaxis.

As already described, the drive units provided for the respective columnselect lines have the same structure, and therefore, FIG. 21representatively shows a structure of drive unit DVU1 corresponding tocolumn select line CSL1.

Referring to FIG. 21, drive unit DVU1 according to the firstmodification of the third embodiment differs from the structure of thedrive unit shown in FIG. 11 in that a delay circuit 265 is furtheremployed.

Delay circuit 265 further delays control signal /WEd sent from delaycircuit 255 shown in FIG. 20 by a predetermined time ΔT to output acontrol signal /WEdd. Control gate 206 outputs results of logical ANDbetween control signals /RE and /WEdd. Control gate 208 applies resultsof logical OR between the outputs of decode unit CDU1 and logical gate206 to each of the gates of P- and N-channel MOS transistors 201 and204, similarly to the structure shown in FIG. 11.

In the structure shown in FIG. 21, the current drive power of P-channelMOS transistor 202 is designed similarly to the current drive power(operation current I2 in FIG. 11) of P-channel MOS transistor 200.Therefore, the drive power (amount of current supply) of column selectline CSL, which is active in the data write operation, is set similarlyto that in the data read operation. Accordingly, the rising rate ofvoltage on active column select line CSL, and thus the rising timeconstant are substantially uniform in each of the data write operationand data read operation.

In each column cycle including instruction of the data write operation,column select line CSL in the selected column is rapidly activated toattain power supply voltage Vcc2, or is rapidly inactivated to attainground voltage Vss in response to control signal /WEdd with a delay oftime ΔT from activation or inactivatation of write word line WWL in theselected row. Predetermined time ΔT in delay circuit 265 is set in viewof a difference between times t0 and tw in FIG. 20 and a differencebetween times t3 and t4 so that data write currents Ip and ±Iw can besupplied in accordance with the timing shown in FIG. 20. The delay timesof delay circuits 255 and 265 may be appropriately determined so thatboth delay circuits 255 and 265 may use common control signal /WE.

In the data read operation, column select line CSL in the selectedcolumn is activated to H-level (power supply voltage Vcc1) in accordancewith the fastest timing responsive to the activation (L-level) ofcontrol signal /RE.

Owing to the above structure, when the page mode operation is performed,the data write magnetic field in the direction of hard axis can likewisebe produce or removed more rapidly than the data write magnetic field inthe direction of the easy axis when the data write operation starts orends in the column cycle, during which the data writing is executed.Thereby, similarly to the first modification of the third embodiment,the data writing can be stably executed with consideration given tomagnetization characteristics of the MTJ memory cell.

Second Modification of Third Embodiment

A second modification of the third embodiment will now be described inconnection with a page mode operation, which allows continuous executionof the data read operation and the data write operation in a mixedmanner over a plurality of column cycles within one unit operationcycle.

Referring to FIG. 22, when the unit operation cycle starts in the pagemode operation according to the second modification of the thirdembodiment, the row cycle for receiving applied row address RA (and bankaddress BA) for row selection is first performed, similarly to the pagemode operation according to the third embodiment and the firstmodification thereof. The results of row selection performed with rowaddress RA (and bank address BA), which is input in this row cycle, areheld in the same operation cycle. Based on the row selection resultsthus held, read word line RWL is activated to attain H-level except forthe column cycle, in which the data write operation is instructed.

In each column cycle, control signal /WE is set to L-level for apredetermined period if the data write operation is instructed.

Referring to FIG. 23, read word line drive portion 30R according to thesecond modification of the third embodiment differs from the read wordline drive portion according to the third embodiment shown in FIG. 19 inthat a pulse generating circuit 280 is employed instead of latch circuit250. Pulse generating circuit 280 produces a control pulse /WCC fordetermining the active period of read word line RWL in accordance withthe level of control signal /WE at the time of activation of clocksignal CLK.

Referring to FIG. 22 again, when control signal /WE is at H-level at thetime of activation of clock signal CLK in a certain cycle, control pulse/WCC is kept at H-level in the same cycle. In the column cycle includinginstruction of data writing, control signal /WE is set to L-level at thetime of activation of clock signal CLK so that control pulse /WWC iskept at L-level for a predetermined period which corresponds to betweentimes t0 and t4 in FIG. 22. This predetermined period depends on, e.g.,the active period of control signal /WE.

Referring to FIG. 23 again, drive units 220-1–220-n control activationof corresponding read word lines RWL in response to the row selectionresults held in latch circuits 260-1–260-n and the inverted signal ofcontrol signal /WCC, respectively. Although not shown in FIG. 23,similar structures are employed for dummy read word lines DRWL1 andDRWL2.

Write word line drive portion 30W has structures similar to those shownin FIG. 19, and controls activation of write word line WWL in theselected row, which corresponds to row address RA (and bank address BA)applied in the row cycle, in every column cycle.

Owing to the above structure, read word line RWL in the selected rowcorresponding to the latch circuit, which holds L-level data, isactivated to attain H-level during a period except for a predeterminedperiod in the column cycle including the instruction of the data writeoperation. This increases the operation speed in each column cycleincluding the instruction of the data read operation.

In column cycles #1 and #2, which include instruction of the data writeoperation, each read word line RWL is inactivated, and the data writeoperation can be performed for the selected memory cell, whichcorresponds to applied column address CA1 or CA2 and row address RA (andbank address BA) applied during the row cycle, similarly to the thirdembodiment and the first modification thereof.

The activation timing of write word line WWL must be set in accordancewith the structure of memory array 10. In the structure having writeword lines WWL, which are electrically isolated from respective MTJmemory cells as shown in FIG. 16, no adverse effect occurs even if writeword line WWL is supplied with the data write current while read wordline RWL in the selected row is active. According to the abovestructure, therefore, such a design may be employed that read and writeword lines RWL and WWL in the selected row are active for periods, whichoverlap with each other when data write operation starts.

In contrast to the above, the memory array shown in FIG. 7. has astructure, in which the current path including both tunnelingmagneto-resistance element TMR and write word line WWL is formed inresponse to turn-on of access transistor ATR. In this structure,erroneous data writing may occur if read and write word lines RWL andWWL in the selected row are active for time periods having overlappingportions. In this memory array structure, therefore, such setting ordesign is required that the active periods of read and write word linesRWL and WWL in the selected row do not overlap with each other.

In the structure according to the second modification of the thirdembodiment, therefore, both the fast data reading and the stable datareading, which is achieved in consideration of magnetizationcharacteristics of the MTJ memory cell, can be executed in the page modeoperation, which allows mixing of the data read operation and the datawrite operation.

Third Modification of Third Embodiment

A third modification of the third embodiment will now be described inconnection with a structure for further increasing a speed of the dataread operation in the page mode operation, which includes the data readoperation and the data write operation in a mixed manner.

Referring to FIG. 24, an MRAM device 2 according to the thirdmodification of the third embodiment differs from MRAM device 1 shown inFIG. 1 in that a read data latch circuit 300 is further employed.

Read data latch circuit 300 latches at least a portion of the data of mbits, which are read by read/write control circuit 50, in response tocontrol signal LS produced by control circuit 5. Further, read datalatch circuit 300 outputs, as read data DOUT, at least one among theplurality of internally latched storage data in accordance with controlsignal RO sent from the control circuit and results of the columnselection of column decoder 25.

The structure for writing write data DIN into the selected memory cellwithin memory array 10 is substantially the same as those of the thirdembodiment and the first and second modifications hereof, and thereforedescription thereof is not repeated.

In the page mode operation according to the third modification of thethird embodiment, as shown in FIG. 25, data reading for one rowcorresponding to the selected row indicated by input row address RA (andbank address BA) is executed during the row cycle. Thus, read word linedrive portion 30R activates read word line RWL in the selected row inresponse to control signal /RC, which is activated to attain L-level fora predetermined period, during the row cycle.

In the row cycle, column select lines CSL of M (M: integer exceeding oneand not exceeding m) in number corresponding to at least a part of allthe memory cell columns are activated in parallel, and data reading isexecuted in parallel on the plurality of memory cells. In general, datareading is executed in all the memory cell columns, or is executed inthe odd-numbered or even-numbered columns.

Read/write control circuit 50 is designed such that supply of the sensecurrent Is and reading of the storage data can be performed in parallelfor the M memory cell columns, which are simultaneously selected. Forexample, the structure for data read circuit 51R shown in FIG. 8 must bedivided into M portions equal in number to the memory cell columns to beactivated simultaneously. In the form of this modification, it isassumed that all the data for one row are read out in parallel, and thusM is equal to m.

In accordance with the timing of production of the m read datacorresponding to the selected row by read/write control circuit 50,control circuit 5 activates control signal LS for a predeterminedperiod. In response to this, read data latch circuit 300 latches theread storage data of m in number.

In the subsequent column cycle #1 including instruction of the datawrite operation, control signal /WE is set to L-level for apredetermined period including the activation of clock signal CLK.Further, column address CA1 for representing the data write target isinput.

In response to this, data write currents ±Iw and Ip are supplied forstably magnetizing the selected memory cell, which corresponds to rowaddress RA (and bank address BA) and column address CA1, in accordancewith the level of write data, similarly to the third embodiment and thefirst and second modifications thereof.

In the column cycle #2 including instruction of the data read operation,control signal /WE is set to H-level in accordance with the activationtiming of clock signal CLK. Also, column address CA2 indicating the dataread target is input.

In column cycle #2, control circuit 5 activates a control signal RO toattain H-level for a predetermined period. In response to this, readdata latch circuit 300 selects one storage data corresponding toreceived column address CA2 from the m storage data latched in the rowcycle based on the results of column selection of column decoder 25, andoutputs the selected data as read data DOUT.

Owing to the above structure, the data read operation in each columncycle can be performed at an increased speed because it is not necessaryto detect the change in voltage on the bit line, which is caused bysense current Is passing through the selected memory cell.

In each column cycle, all read word lines RWL are inactivated to attainL-level. Therefore, even in the column cycle including instruction ofthe data write operation, write word line WWL can be activated inaccordance with the fastest timing, and the data write operation canstart fast.

According to the structure of the third modification of the thirdembodiment, the page mode operation already described in connection withthe third embodiment and the first and second modifications can beperformed further rapidly while performing the data read operation andthe data write operation in a mixed manner.

The page mode operation already described in connection with the thirdembodiment and the first and second modifications thereof can likewisebe applied to a structure, in which column select lines for reading areindependent of those for writing.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A thin-film magnetic memory device for executing a page modeoperation with a unit operation cycle including a row cycle forreceiving input of a row address and a plurality of subsequent columncycles for receiving input of a column address in each of said columncycles, comprising: a plurality of memory cells arranged in rows andcolumns, and each having a magnetic memory portion having an electricresistance varying in accordance with a magnetization directionrewritable in response to application of a predetermined data writemagnetic field produced by first and second data write currents; aplurality of first data write interconnections provided for memory cellrows, respectively, for passing said first data write current in aselected row; a plurality of second data write interconnections providedfor memory cell columns, respectively, for passing said second datawrite current in a selected column; and a row select portion forcontrolling supply of said first data write current to said plurality offirst data write interconnections, said row select portion temporarilystopping supply of the first data write current corresponding to saidselected row in response to every ending of said column cycle.
 2. Thethin-film magnetic memory device according to claim 1, wherein said rowselect portion includes: a latch circuit for holding row selectionresults corresponding to said row address applied in said row cycle, anda drive unit for activating said first data write interconnectioncorresponding to said selected row to pass said first data write currentin accordance with said row selection results held by said latch circuitand a control signal for selectively instructing a data write operationand a data read operation.
 3. The thin-film magnetic memory deviceaccording to claim 1, wherein one of said first and second data writecurrents produces a magnetic field along a easy axis in said magneticmemory portion, the other of said first and second data write currentsproduces a magnetic field along a hard axis in said magnetic memoryportion, and a rising time constant of said one of the data writecurrents is larger than that of the other data write current in each ofsaid column cycles including instruction of the data write operation. 4.The thin-film magnetic memory device according to claim 3, wherein eachof said magnetic memory portions has a form having an aspect ratiolarger than one between a long side and a short side, one of said firstand second data write interconnections carrying said one of the firstand second data write currents is arranged along said short side, andthe other of said first and second data write interconnections carryingsaid the other of the first and second data write current is arrangedalong said long side.
 5. The thin-film magnetic memory device accordingto claim 1, wherein one of said first and second data write currentsproduces a magnetic field along a easy axis in said magnetic memoryportion, the other of said first and second data write currents producesa magnetic field along a hard axis in said magnetic memory portion, andsupply of said one of the first and second data write currents startslater than the supply of said the other of the first and second datawrite current in each of said column cycles including instruction of adata write operation.
 6. The thin-film magnetic memory device accordingto claim 5, wherein each of said magnetic memory portions has a formhaving an aspect ratio larger than one between a long side and a shortside, said one of the first and second data write interconnectionscarrying said one of the first and second data write currents isarranged along said short side, and the other of said first and seconddata write interconnections carrying said the other of the first andsecond data write current is arranged along said long side.
 7. Athin-film magnetic memory device for executing a page mode operationwith a unit operation cycle including a row cycle for receiving input ofa row address and a plurality of subsequent column cycles for receivinginput of a column address in each of the column cycles, comprising: aplurality of memory cells arranged in rows and columns, each of saidmemory cells including a magnetic memory portion having an electricresistance varying in accordance with a magnetization directionrewritable in response to application of a predetermined data writemagnetic field produced by first and second data write currents, and anaccess element electrically coupled in series to said magnetic memoryportion, and being selectively turned on for passing a data readcurrent; a plurality of data write select lines provided correspondingto the memory cell rows, respectively, and being selectively activatedto pass said first data write current; a plurality of data read selectlines provided corresponding to said memory cell rows, respectively, andbeing selectively activated to turn on said access element; a pluralityof data lines provided corresponding to the memory cell columns,respectively; a read/write control circuit for supplying said data readcurrent to the data line corresponding to the received column address ineach of the column cycles including instruction of a data readoperation, and supplying said second data write current to the data linecorresponding to the received column address in each of the columncycles including instruction of a data write operation; and a row selectportion for controlling activation of said plurality of data writeselect lines and said plurality of data read select lines in accordancewith results of the row selection based on said row address, whereinsaid row select portion inactivates the data read select linecorresponding to said selected row, and activates the data write selectline corresponding to said selected row for a predetermined period ineach of said column cycles including instruction of said data writeoperation.
 8. The thin-film magnetic memory device according to claim 7,wherein said row select portion activates the data read select linecorresponding to said selected row during a period other than saidpredetermined period.
 9. The thin-film magnetic memory device accordingto claim 8, wherein each of said memory cells is arranged to have a nodeelectrically coupled to the corresponding data write select line, saidrow select portion controls activation of said plurality of data readselect lines such that the active period of said data read select linedoes not overlap in time with the supply period of said first data writecurrent.
 10. The thin-film magnetic memory device according to claim 8,wherein each of said memory cells is electrically isolated from thecorresponding data write select line, and said row select portioncontrols activation of said plurality of data read select lines suchthat the active period of each of said data read select lines has aportion overlapping in time with the supply period of said first datawrite current.
 11. A thin-film magnetic memory device for executing apage mode operation with a unit operation cycle including a row cyclefor receiving input of a row address and a plurality of subsequentcolumn cycles for receiving input of a column address in each of thecolumn cycles, comprising: a plurality of memory cells arranged in rowsand columns, each of said memory cells including a magnetic memoryportion having an electric resistance varying in accordance with amagnetization direction rewritable in response to application of apredetermined data write magnetic field produced by first and seconddata write currents, and an access element electrically coupled inseries to said magnetic memory portion, and being selectively turned onfor passing a data read current; a plurality of data write select linesprovided corresponding to the memory cell rows, respectively, and beingselectively activated to pass said first data write current; a pluralityof data read select lines provided corresponding to the memory cellrows, respectively, and being selectively activated to turn on saidaccess element; a plurality of data lines provided corresponding to thememory cell columns, respectively; and a row select portion forcontrolling activation of said plurality of data write select lines andsaid plurality of data read select lines in accordance with results ofthe row selection based on said row address, said row select portionactivating the data read select line corresponding to a selected row insaid row cycle, and inactivating said data read select line in saidcolumn cycle; a read/write control circuit for supplying said data readcurrent to each of the data lines of at least M (M: integer larger thanone) in number among said plurality of data lines in said row cycle, andsupplying said second data write current to the data line correspondingto the received column address in each of said column cycles includinginstruction of a data writing operation; a read data latch circuit forholding the storage data of M in number corresponding to the M datalines, respectively, and reading from the memory cells belonging to saidselected row in said row cycle; and a control circuit for instructingoutput of one of the M storage data corresponding to the received columnaddress to said read data latch circuit in each of said column cyclesincluding instruction of a data read operation.